Exemplary embodiments of the present invention relate to an oil filter apparatus for use in conjunction with an internal combustion engine. More particularly, exemplary embodiments of the present invention relate to an oil filter apparatus including both a mechanically active filter element and a chemically active filter element incorporated therein.
Oil has a number of important functions in an internal combustion engine. The motor oil lubricant reduces friction that causes wear on metallic components, dissipates heat, seals the combustion chamber, and cleans the engine space by dissolving and dispersing impurities.
Nevertheless, it is well known that during normal operation of an internal combustion engine, particularly a diesel engine, motor oils become contaminated during operation from accumulating combustion particles, foreign substances and abrasion particles. These contaminants include, among other substances, soot, which is formed from incomplete combustion of the fossil fuel, and acids that are a by product of combustion. Both of these contaminants are typically either introduced into the lubricating oil with exhaust gas in the form of blow-by or deposited on cylinder walls and subsequently deposited into the oil. This contamination tends to increase oil viscosity and to generate unwanted engine deposits, leading to increased engine wear. Increased viscosity leads to higher temperatures, higher pumping costs, and the risk of lubricant starvation, especially at start-up. For these primary particles not to cause any damage inside the internal combustion engine, they must be removed from the oil circulation system.
The conventional solution to soot-related problems has been to place various soot agglomeration resistant dispersant additives into lubricating oils. These dispersants may be corrosion inhibitors, antioxidants, friction modifiers, pour point depressants, detergents, viscosity index improvers, anti-wear agents, and/or extreme pressure additives. Dispersants control contamination by attaching themselves to contaminant particles and holding them in suspension. The suspended particles are so finely divided that they pass harmlessly between mating surfaces and through oil filters. The contamination, however, is not actually removed from the engine system until the oil is changed.
With conventional additive methods, the amount and concentration of dispersants are limited by the ability of lubricating oils to suspend the additives, as well as by the chemical stability of these dispersants in the oil. Thus, dispersants work well for a short period, providing once-through protection, but once the dispersants are depleted, the engine left at risk. Additionally, due to the solubility and chemical stability limits of dispersants in the oil, the service lives of the lubricating oil and the oil filter are less than optimal.
To counteract the effects of acidic combustion related problems, many conventional systems include neutralizing additives known as over-based detergents. These are a source of TBN (total base number), which is a measure of the capacity of the oil to neutralize acids. As a quantity of lubricating oil neutralizes acidic combustion products, the oil's ability to do so, that is, its TBN, is gradually reduced, necessitating an oil change. The depletion of the TBN is an important limiting factor for many internal combustion engines, particularly for heavy-duty diesel engines.
Oil conditioning techniques have been used as an alternative to the conventional method of mixing additives with lubricating oil for removing soot and acid contaminants from the oil. Oil conditioning employs filtration to remove contaminants from lubricating oils. Filtration systems chemically and/or mechanically separate insoluble particulate matter from a fluid by passing the fluid through a filter medium that will not allow the particulates to pass through. Most such filters use a mechanical or ‘screening’ type of filtration, with a replaceable cartridge having a porous filter element therein, through which the oil is repeatedly cycled to remove impurities. An oil-conditioning filter protects the engine from harmful particles by repeatedly cycling the engine's lubricating oil therethrough.
For example, in order to combat the build up of sludge in oil, U.S. Pat. No. 5,478,463 (“the '463 patent”) and U.S. Pat. No. 5,042,617 (“the '617 patent”) both disclose an oil filter and a method for reducing the amount of sludge in lubricating oil as it circulates throughout an engine. These patents provide for the inclusion of particles in an oil filter that are oil insoluble and oil wettable, and which complex with sludge so that at least some of the sludge that these particles come into contact with is immobilized on the particles. The '617 patent discloses the inclusion of oil insoluble and oil wettable particles in an oil filter that are retained on a pelletized substrate, whereas the '463 patent discloses the inclusion of such particles that are not retained on a substrate, but are nonetheless retained in the oil filter.
Analogously, U.S. Pat. No. 5,069,799 (“the '799 patent”) discloses an oil filter and method for reducing the amount of combustion acids in lubricating oil. In particular, the '799 patent discloses a method of rejuvenating lubricating oil, which includes reducing combustion acids, by serially passing the oil through first a chemically active filter media, then a physically active filter media, and finally an inactive filter media. In this patent, the chemically active filter media includes a strong base to displace weak bases that have combined with combustion acids. The combustion acid and the strong base then combine to form a salt that is subsequently trapped by mechanical filter media.
U.S. Pat. No. 5,225,081 (“the '081 patent”) discloses a method of removing polynuclear aromatics from used lubricating oil. The method of the '081 reference involves passing oil through a staged oil filter system that may include a chemically active filter media. The chemically active filter media is made of a composite material that includes particles of an active component and a thermoplastic binder, which are products of a heated extrusion process. Basic conditioners are given as one example of materials suitable for use as chemically active filter media. Activated carbon is also emphasized as being a preferred component of the filter media.
Some designs for multiple stage oil filters are known, such as those disclosed in U.S. Pat. Nos. 4,557,829 and 4,886,599, These patents disclose a filter cartridge with sequential concentric cylindrical filter elements, for both chemical and mechanical filtration of oil contained in an oil-sealed vacuum pump.
Other designs for oil filters that contain extra additives and dispense those additives into oil, over time, are disclosed in U.S. Pat. Nos. 4,075,098 and 5,552,040.
While the above discussed methods for removing soot and acid contaminants from lubricating oil are usable for their intended purposes, the prior art fails to account for engine modifications such as exhaust gas recirculation (EGR) that are being incorporated as more rigorous exhaust emission regulations continue to be adopted and enforced.
EGR is a NOx (nitrogen oxide and nitrogen dioxide) reduction technique that is used in most gasoline and diesel engines and works by recirculating a portion of an engine's exhaust gas back into the intake stream. Exhaust gases have already combusted, so they do not burn again when they are recirculated. Intermixing the incoming air with recirculated exhaust gas dilutes the mix with inert gas, thereby slowing and cooling the combustion process by several hundred degrees, and (in diesel engines) reducing the amount of excess oxygen. Because NOx formation progresses much faster at high temperatures, EGR serves to limit the generation of NOx.
While processes such as EGR serve to reduce exhaust emissions into the atmosphere, the recirculated engine emission loads are returned to the combustion chamber and collected in the lubricating oil, thereby resulting in rapid TBN depletion due to acid formation and the generation of dramatically higher levels of soot during combustion. Thus, particularly because of the acids formed in the oil as oxidation products as well as the acidic nature of the blow-by gas, the use of EGR can significantly reduce the useful life of the engine's lubricating oil.
Accordingly, there is a need for an improved oil conditioning filter that can extend the useful lubricating oil life in a vehicle equipped with an EGR system, particularly a vehicle having a diesel engine, so as to allow a user to extend the time interval between oil changes in a vehicle.